Mdf press technology

ABSTRACT

The invention relates to a method for the production of a construction element manufactured from wood fibers, matchwood and/or sawdust, especially a board, comprising the following steps: adhesive is applied to the wood fibers, matchwood and/or sawdust; the wood fibers, matchwood and/or sawdust provided with adhesive are pressed to form a construction element, especially a board.

The invention relates to a construction element manufactured from woodparticles such as fibres or chips. A method is specified for themanufacture of construction elements. In particular, the inventionrelates to boards made entirely or predominantly from wood fibres.

A method for the manufacture of a wood-fibre board is already known fromthe German specialist periodical HK 1/88, pp 74 to 75, “Manufacture ofMDF-Boards”. Boiled wood chips supplied to a so-called refiner. In therefiner, the wood chips are processed by means of grinding discs to formfibres, in fact, subject to the additional supply of temperature andpressure. The fibres are removed from the refiner by means of steam andtransported via a line known as a “blow line”. In this context, thesteam pressure is approximately 10 bar. The temperature is approximately150 to 160° C. Adhesive is added in the “blow line”. Phenol resins, urearesins or mixed resins made from urea and melamine can be used as theadhesive. After the addition of adhesive, the “blow line” becomes wider.Turbulence is caused by this widening, and the adhesive is mixed withthe fibres. The proportion of adhesive to fibres is approximately 22% byweight.

The “blow line” opens into the centre of a drying tube. The drying tubehas a diameter of, for example, 2.60 m. Air is blown through the dryingtube at a temperature of 160° C., with a maximum of 220 to 240° C. Inthe drying tube, the moisture is reduced from 100% to 8 to 11%. Theresulting steam charged with non-aqueous substances is separated fromthe fibres in subsequent cyclones and released into the environment viachimneys.

The fibres provided with adhesive are supplied in the form of layers toa moulding machine, where the fibres are pressed in two phases.Initially, a preliminary pressing takes place. The pre-pressed fibresare then compressed under high pressure with a supply of heat to form aboard. Specialists in this field have determined that the boards split,if the temperature during pressing to form a board falls below 150° C.,for example, to 140° C. During pressing, the temperatures are thereforetypically in the region of 180° C.

Additional known details, which could be of interest for the manufactureof wood-fibre boards are outlined below. An adhesive-application devicefor the production of fibre boards is known from the specification EP 0744 259 A2. A method for manufacturing boards from a timber material isknown from the specification U.S. Pat. No. 5,554,330. The document GB791,554 discloses a method for mixing solid and liquid components. Adevice for the continuous application of adhesive to wood chips isdisclosed in DE 41 15 047 C1. Continuous mixing of materials in the formof chips and fibres with bonding agents is disclosed in DE-OS 1956 898.The specifications PCT/IB98/00607 and WO 98/37147 disclose the recoveryof adhesive from timber components. Preliminary steam-treatment methodsare disclosed in DE-OS 44 41 017, U.S. Pat. No. 111,795 and in theDanish patent No. 0302/97.

The object of the present invention is to reduce manufacturing costs.

The object of the invention is achieved by one of the methods claimed. Aboard manufactured according to the method comprises the features of thedependent claim.

According to general expert opinion, wood-fibre boards must be pressedat temperatures above 150° C., because it has been established, thattemperatures below 150° C. lead to defects in the surface. The boardssplit, if the temperature falls below 150° C., and cracks appear. If atemperature of 150° C. is exceeded during pressing, splitting is avoidedas a result of an adequate hardening of the adhesives and/or resinsused.

The inventors have established that it is exclusively the steamoccurring at the high temperatures, which is responsible for thesplitting. No splitting occurs, if steam is not produced at all, or, atleast, if steam is produced only to a slight extent because ofsufficiently low temperatures.

Surprisingly, it was also found that splitting can be avoided byselecting sufficiently low temperatures during pressing. It is importantthat no steam or only a small amount of steam is produced duringpressing. Temperatures below 120° C. have already proved adequate. Thetemperature range between room temperature and 95° C. is preferred. Byparticular preference, pressing is carried out at temperatures up to 60°C. The rate of pressing is not influenced or hardly influenced by thesupply of heat. However, a delay can occur in pressing, if, for example,the wood components are only brought up to temperature in the press. Inthis case, a delay occurs because heating requires time.

If the fibres with the resin are pressed at temperatures, for example,of 200° C., then the resins, which are typically used, harden completelyor almost completely. The resin does not harden or hardens only to aninsignificant extent, if it is pressed together with the wood chips,wood fibres, sawdust or mixtures thereof at temperatures below 120° C. Aperson skilled in the art was previously of the opinion that resin oughtto harden so that a surface, which is free from defects, can be achievedin construction elements such as boards made from timber materials.

The resins used are initially present in the form of low-molecularweight components. Hardening means that the low-molecular weightcomponents cross-link with one another, thereby forming a stablenetwork.

The construction element manufactured according to the method differsfrom the prior art, in particular, in that the resins used are nothardened. The resin used can be detected in an unchanged or almostunchanged state by chemical analysis of the product. Accordingly, nochemical change and no chemical cross-linking or practically no chemicalcross-linking has taken place.

The board manufactured at sufficiently low temperatures can, inparticular, be used as a semi-finished product. In one embodiment of theinvention, this board is fed into a press in a known manner togetherwith decor paper, counteracting paper and other components of a laminateflooring. Pressing is then carried out at temperatures above 150° C.,preferably above 180° C. The upper temperature limit is reached, whenthe temperature causes damage to the product.

In this manner, not only are the papers connected to the board, but theresins in the board are also hardened. Altogether, considerable costsavings are achieved, because one heating stage has been reduced or evencompletely eliminated.

A typical density of the board manufactured according to the inventionis around 650 kg/m³. The board should be pressed so strongly, that thedensity does not fall below 300 kg/m³, preferably 400 kg/m³, byparticular preference 500 kg/m³, in order to achieve a stable andtherefore easily-handled board. The density of the board is typicallybelow 1000 kg/m³.

When the board is pressed to form the end product, for example, a coatedboard for laminate flooring, it can be compressed to a density above1500 kg/m³, by particular preference to a density above 2000 kg/m³.Accordingly, the density in one exemplary embodiment is 2400 kg/m³.

The proportion of resin in the board is, for example, around 7.5% byweight, if the manufactured board is to be used as flooring in the formof panels. In the case of door panels, the proportion of resin istypically 2.5% by weight. To manufacture boards which satisfy the EN438standard, the proportion of resin should not exceed 35% by weight. Foreconomic reasons, the limit of approximately 10% by weight resin shouldnot be exceeded. A lower limit at which the method still functions, isapproximately 1% by weight.

The resins used are reactive resins, that is to say resins withcomponents, which are chemically capable of forming a network. Examplesof reactive resins include: solid or liquid phenol resins, amino resins,for example, urea resins, melamine resins, acrylic resins, epoxy resinsand/or polyester resins.

In one embodiment of the invention, wood chips made from timber canfirst be separated into solid and liquid components. The solid woodcomponents are dried and provided with adhesive, that is to say,reactive resins. The solid wood components provided with adhesive arethen pressed to form a moulded body, for example, a board.

The liquid components comprise, in particular, lignin and hemicellulose.At the temperatures predominating during drying, these substancesproduce emissions, which cause odour pollution and therefore alsoenvironmental pollution. By separating these liquid components beforedrying, the corresponding emissions during and/or following drying arereduced. Environmental pollution during the manufacture of the boards isreduced correspondingly.

The liquid components are preferably disposed of and/or furtherprocessed at temperatures, at which only minimal emissions occur. If thetemperatures of the liquid components are high, in particular, if thesetemperatures are above 90° C., then the liquid components are held in agas-tight system sealed from the environment until the temperatures havefallen sufficiently.

In a further embodiment of the invention, the liquid components, inparticular lignin and hemicellulose, are used as an adhesive, that is tosay, according to the invention, these components are mixed with thedried, solid wood components. The solid wood components are preferablyfurther processed to form fibres or chips. The liquid components may,for example, be separated from the solid wood components in a so-calledagitator. The components named above, are typically obtained in thefollowing proportions: 20 to 35% by weight hemicellulose, 45 to 50% byweight cellulose and 20 to 35% by weight lignin. The cellulose is asolid component of the wood.

In one embodiment, wood chips are first placed in a packing screw. Fromthe packing screw, the wood chips are conveyed in a compressed conditionto a boiling container where they are boiled under high pressure. Theboiling container is therefore designed for high pressures. The pressurein the boiling container is, in particular, at least 1.2 to 2.2 MPa (12to 22 bar). According to the prior art, wood chips are generally boiledat pressures of only 0.8 to 0.9 MPa. As a result of the steam-temperingtreatment, the solid wood components (cellulose) are separated from thelignin and hemicellulose, which provide the liquid components. Thecellulose is present in solid form. The two other components lignin andhemicellulose are liquids and can, in principle, be used as an adhesive.The adhesive force in this case is achieved primarily by thehemicellulose.

It is, in fact, already known from the specification WO 98/37147, thatthe lignin and hemicellulose contained in wood can be separated from thesolid components and subsequently used as an adhesive for themanufacture of MDF boards. However, the disadvantage with this method isthe strong emissions, which pollute the environment around a productionsite. According to the invention, the problem of emissions is reduced,in that the liquid components are separated from the solid components ofthe wood in a gas-tight container. The liquid components are separatedand initially remain, for example, within a gas-tight system connectedto the container, in fact, at least while the temperatures of the liquidare sufficiently high to cause strong emissions. After the separation ofthe liquid components, these cool down to a significant extent and areonly removed from the gas-tight system at relatively low temperatures,for example, for further processing, especially by spraying via nozzlesonto the fibres. The liquid components are therefore significantlycooled, in particular, by at least 30° C., preferably by at least 50°C., before they leave the gas-tight and therefore also odour-tight,sealed system. In this relatively cool condition, the development ofodour is significantly reduced. Removal of the liquid components fromthe gas-tight system is then non-critical.

The liquid components can be used as an adhesive. This is achieved in anenvironmentally-friendly manner in that the liquid components of a woodare only removed from a gas-tight and therefore odour-tight, sealedsystem at low temperatures, especially at temperatures significantlybelow 100° C., especially below 70° C., by a particular preference below50° C., and applied to the fibres, for example, in this cool condition.

Environmental pollution can thus be reduced in a particularly economicalmanner.

The gas-tight system consists, for example, of the container togetherwith the connected lines. A further container, which can be used, forexample, for cooling, may also form part of the gas-tight system.

With a treatment according to the prior art, the adhesive is undesirablysubjected to a temperature treatment in the drying tube. Fromapproximately 80° C. the adhesive is, in fact, disadvantageouslystressed and/or activated. Activated adhesive can no longer be used forthe subsequent processing stage, in which the glued, solid woodcomponents are compressed to form the board.

With the prior art mentioned above, the active component of the adhesiveis reduced. Of the original 22% by weight normally used, only 1 to 8% byweight is available for use, after the fibre-adhesive mixture is removedfrom the drying tube. According to the invention, the adhesive isapplied to the solid wood components in a relatively cool condition.This avoids any unnecessary, premature and extensive activation of theadhesive.

An adhesive based on formaldehyde-urea is currently used in HDF boards,MDF boards and chip boards. Melamine is added to the adhesive, if theboards are to be used for flooring. This prevents swelling, which canoccur as a result of moisture.

The problem here is that some of the adhesive is lost for the actualprocessing stage as a result of the temperature treatment. It istherefore a disadvantage that considerably more adhesive must be addedto the fibres or the chips, than is necessary in order to press thefibres or the chips in a press with a supply of heat and in order toachieve the desired outcome, such as, an MDF board. At present, an MDFboard can contain approximately 60 kg of adhesive per m³. This quantitycan be considerably reduced, if the adhesive is applied in a relativelycool condition.

In one embodiment of the invention, the liquid components, hemicelluloseand lignin, obtained in the manner described above, are applied as anadhesive to the solid wood components in a cooled or cool condition. Inthe cooled or cool condition, these components can advantageously bemixed with another adhesive. In this case, the other adhesive is notobtained from the liquid components of the wood. The proportion ofhemicellulose and lignin in the adhesive mixture prepared in this manneris preferably no more than 20% by weight. Furthermore, the mixtureespecially contains an adhesive based on formaldehyde-urea. Moreover,the adhesives specified in the prior art can be used.

If an adhesive mixture, which contains more than 20% by weighthemicellulose and lignin, is used, then the pressing time (with asupplementary use of currently available, conventional syntheticadhesives), during which the glued fibres are pressed to form a board,is relatively long. It is therefore more economical, to mix thehemicellulose and lignin with another adhesive or adhesive mixture. Onthe one hand, conventional adhesive can be saved, and on the other hand,the method is not relatively prolonged, thereby becoming lesseconomical, because of the long pressing times. The economicallymeaningful upper limit for the proportion of hemicellulose and lignin isdependent upon the reactivity of the adhesive, with which thehemicellulose and lignin components are mixed. The named upper limit of20% by weight therefore merely represents a guide value or respectivelya value based on current experience.

In one embodiment of the invention, the solid wood components are firstdried, and adhesive is then mixed with the dry components attemperatures, which are considerably lower than the drying temperatures,in particular below 100° C. This avoids exposing the adhesive toundesirable, relatively hot temperatures, which occur during drying.With the prior art, the adhesive also contributes to emissions. Sincethe adhesive is now no longer exposed to hot drying temperatures, but isapplied to the solid wood components at relatively cool temperatures,emissions originating from the adhesive are also avoided. In the drierand/or drying tube, only water but not chemicals are dried.Corresponding environmental advantages result from this, because the dryair is not disadvantageously charged with vapours originating from theadhesive, as in the prior art. The manufacture of the boards istherefore more environmentally friendly. This embodiment has theadditional advantage that proportions of the adhesive are notdisadvantageously activated during the drying process and thereforeunavailable for the actual gluing of the wood components to form theboard.

The solid wood components, which are present particularly in the form offibres or chips, and which are dried, are also advantageously notcharged with liquid components of the wood material and, in theembodiment named above, also not charged with adhesive. Thecorresponding liquid phases are therefore also not dried in the drier.By comparison with the prior art, considerable energy savings areachieved. The saving of energy not only leads to considerable costadvantages, but also protects natural resources and therefore theenvironment.

Because the adhesive is only applied to the wood components afterdrying, the quantity of adhesive required for the manufacture of theboards is reduced. A reduction to 45 to 55 kg/m³ board can be achieved.A typical value is around 50 to 52 kg/m³ of board.

One essential parameter in order to achieve a suitable gluing of fibresor chips is the “correct” ratio of the solid wood components to theadhesive. In one embodiment of the method according to the inventiontherefore, the solid wood components are supplied to a belt weighingmachine before the application of the adhesive. On the belt weighingmachine, the solid wood components are not only transported by means ofa circulating conveyor belt, they are also weighed. As a result,information is obtained regarding the quantity of adhesive to be addedto the solid components of the wood in the following stage.

The solid wood components are transferred to the subsequent device bymeans of the belt weighing machine. In one embodiment, possiblefluctuations in the weight of the solid wood components supplied aremeasured, registered and stored during transport. These data areprepared and can be used as parameters for adjusting the quantity ofadhesive, which is subsequently applied to the solid wood components.

In one embodiment of the invention, the rate of transport on the beltweighing machine is controlled in such a manner that a uniform quantityof solid wood components is supplied to the downstreamadhesive-application device (in which the solid wood components areprovided with adhesive). By changing the rate of the feeder, a constantquantity of material can be supplied to the downstream devices. Theweight of the solid wood components, which may be present in the form offibres or chips, can be registered in extremely small steps. This allowsa uniform supply of the solid wood components with an accuracy, forexample, of ±1%.

It is not easy to provide the solid wood components with adhesive in auniform manner, especially if the solid wood components are present inthe form of fibres. Fibres have a tendency to clump together in the formof a wad. It is then difficult to distribute the adhesive uniformly onthe fibres. In one embodiment of the invention, the application of theadhesive is carried out in a mixer, in which the adhesive and the solidwood components are mixed with one another.

In one embodiment of the invention, the mixer provides means for coolingits housing. For this purpose, in one particularly simple embodiment, anat least partially double-walled housing, for example, a double-walledtube, which forms a part of the housing of the mixer, is provided. Acooled liquid, for example, cooled water, is supplied through thedouble-walled housing, in order to cool the mixer or respectively itswalls. As a result of the cooling, a layer of condensation water isformed on the walls. The cooling is designed accordingly. As a result ofthe layer of condensation water, solid wood components provided withadhesive do not adhere to the walls and clog the mixer.

After drying, the solid wood components are spread, according to oneembodiment of the invention, in a flat manner, forming a type of curtainor mat. This is especially appropriate if the solid wood components arepresent in the form of fibres, because a mat and/or a curtain canreadily be formed from fibres. Adhesive is then added, in particular,sprayed onto the curtain. By preference, an air-adhesive mixture issprayed, in order to guarantee the most uniform possible distribution ofthe adhesive. As a result of the formation of a curtain, the adhesive isdistributed uniformly on the solid wood components. This is particularlyappropriate if the solid wood components are present as fibres.

In one embodiment, a curtain or mat formed from solid wood components isfed into the mixer. An air-adhesive mixture is then blown throughnozzles onto the curtain or mat. The adhesive is therefore supplied tothe curtain or mat via the nozzles. Following this, the curtain or matis transported through the mixer preferably in a contactless manner.Contactless transport advantageously prevents the adhesion of the solidwood components to the walls. Problems of contamination and theassociated costs are therefore reduced.

Together with air, the adhesive is blown into the dried solid woodcomponents, especially at a temperature from 40 to 70° C., preferably ata temperature from 55 to 60° C. This means that the adhesive reaches adry exterior skin. Accordingly, it is activated only to a minimalextent. As a result, the subsequent mixture of solid wood components andadhesive does not adhere to transport equipment and devices, forexample, in the interior of the mixer.

Because the adhesive is exposed to considerably lower temperatures thanhitherto, it is possible to use more reactive adhesives by comparisonwith the prior art. Moreover, it is possible to reduce the proportion ofchemicals such as formaldehyde. This leads to further environmentaladvantages.

In one embodiment of the invention, the adhesive is brought intoturbulence with heated air, and this air-adhesive mixture is supplied tothe dried, solid wood components, for example, fibres or chips. Theheated air, which is supplied to the mixer, for example, together withthe adhesive and the dried, solid wood components, via a cabin or cell,to a certain extent activates the surfaces of the adhesive dropletsformed in this manner. As a result, an adhesion of the solid woodcomponents to downstream devices, for example, to the walls of themixer, is appropriately prevented. Otherwise, the mixer would have to becleaned, for example, after very short intervals, therebydisadvantageously interrupting production. Undesirable cleaning costswould also be incurred. Regarding the disadvantage, that the adhesive isslightly activated, the considerable economic disadvantages referred toabove must be evaluated and weighed against one another. With a fewexperiments, a person skilled in the art can determine the extent, towhich the surface of the adhesive should be activated in order toachieve an optimum economic result. The proportion of activated adhesivewill always be small by comparison with the prior art.

In one embodiment of the invention, in order to facilitate subsequentprocessing stages, the free surface of the adhesive is somewhat furtheractivated after the adhesive has been added to the dried solid woodcomponents such as fibres or chips by means of a device suitable forthis purpose. After the adhesive has been added to the dried, solid woodcomponents, that is, to the fibres or chips, especially after leavingthe mixer, the solid wood components provided with the adhesive arepreferably conveyed into an ascending pipe, which is, in particular, 10to 30 m long, by preference, approximately 20 m long. The diameter ofthe ascending pipe is, in particular, from 1 to 4 m.

The ascending pipe is preferably also cooled and is, for example, alsodouble walled in order to allow a flow of cooling liquid between the twowalls. Once again, the aim is to form a layer of condensation water onthe interior walls of the ascending pipe, so that the glued solid woodcomponents do not adhere to the walls.

The glued, solid wood components can be conveyed through the ascendingpipe in a particularly simple, contactless manner, by means of an air orgas flow.

It has been shown that the solid wood components, especially if theseare present in the form of fibres, should be conveyed through theascending pipe at a rate of at least 25 m per second, preferably atleast 35 m per second. At a slower rate, the fibres or chips wouldadhere more intensively to the ascending pipe in spite of the measuresmentioned above. As a result, the ascending pipe would be contaminatedunnecessarily quickly. With slower rates, the ascending pipe had to becleaned after 8 hours. By adjusting an appropriate rate, the cleaningcycles were extended to 7 to 8 days. Accordingly, the ascending pipeneed only be cleaned once a week.

The maximum rate, at which the solid wood components provided withadhesive are blown through the ascending pipe, depends upon theperformance of the equipment and/or devices downstream. In this context,it must be taken into consideration that the downstream equipment and/ordevices must be capable of processing the incoming quantity of solidwood components. In practice, at present, an upper limit of 40 m persecond can be realised without difficulty. From 50 m per second,currently used downstream equipment was overloaded. The upper speedlimit can be increased, as soon as downstream equipment of higherperformance is available. In principle, faster transport rates in theascending pipe are advantageous, because problems of contamination andthe associated interruption of production are reduced accordingly.

Providing an ascending pipe means that the adhesive is further activatedto some extent on the surface, in order to allow the implementation ofdownstream processing stages in an appropriate manner. The length of theascending pipe should therefore be adapted by the person skilled in theart to the desired degree of adhesive activation. The person skilled inthe art will take the rate of transport through the ascending pipe intoaccount within the design process.

Following the addition of adhesive to the dried, solid wood components,in particular, following the partial activation of the adhesive in theascending pipe, the solid wood components, which are provided withadhesive, are transported into a cyclone. Here, the surface of theadhesive has been activated adequately as a result of the measures namedabove, so that it does not adhere in the cyclone. In the cyclone, thesolid wood components are separated and transported to the nextprocessing stage by a transport means such as a conveyor belt. The solidwood components are separated from the air in the cyclone. In oneembodiment, the transport means conveys the solid wood components into ascreening device. In the screening device, the solid wood components arescreened for coarse components. Any coarse components are automaticallyremoved. Coarse components include, for example, lumps of adhesive.

From the screening device, the solid wood components are transported bya belt to the press, where they are compressed to form a board. Thepress preferably consists of circulating compression belts pressedagainst one another, which are tempered appropriately. This allowscontinuous pressing. The temperature should be adjusted for the relevantadhesive by a person skilled in the art. According to one embodiment,the quantity of energy and the resulting temperatures for the twocompression belts are selected to be different, in order to prevent adistortion of the board manufactured. However, according to theinvention, a tempering of the press can also be completely omitted.

In one embodiment of the invention, the nozzles through which theadhesive is supplied to the solid wood components are preferablydesigned to be conical. The adhesive then emerges from the tip of thecone in the form of droplets, thereby advantageously promoting andimproving a uniform distribution of the adhesive.

To avoid cleaning work and an associated interruption of production,attention should be paid to the fact that the adhesive emerging, forexample, from nozzles, does not come into contact with downstream tools,such as tools disposed in the mixer. The adhesive is thereforepreferably directed, in particular, sprayed, towards the solid woodcomponents in order to achieve the most uniform possible distribution.Moreover, it is particularly important to ensure an adequate distancebetween the nozzles and the tools downstream in the mixer. In practice,it has been shown that the distance between the tools in the mixer andthe nozzles should be at least 1 m, preferably at least 2 m, if theadhesive is sprayed in a horizontal direction. The solid wood componentsare then introduced vertically at the start of the mixer and furthertransported within the mixer in a horizontal direction. The actualdistance values named relate, of course, only to an individual exemplarycase. They are not generally applicable, because these values areultimately dependent upon the rate, at which the adhesive emerges fromthe nozzles.

If an air-adhesive mixture is sprayed towards the solid wood components,an air stream, by means of which the solid wood components can be blownand therefore transported, initially with the minimum possible contact,through the downstream devices such as a mixer or an ascending pipe, isadvantageously provided at the same time. Another gas may in principlealso be used instead of air.

Stirring devices, which achieve a mixing of the solid wood componentswith the adhesive are used, in particular, as the tools within themixer.

To achieve good results, the solid wood components are brought in frontof the nozzles in the form of a curtain. Accordingly, in addition to theadvantages already named, this prevents the adhesive from being sprayedinto the mixer and contaminating the tools disposed there. Otherwise,the solid wood components would adhere to the tools, and the mixer wouldbecome clogged in a very short time and would have to be cleaned inshort intervals.

In one embodiment, the tools in the mixer are attached to a centrallymounted axis and consist of rods projecting in a star-shape, each ofwhich merges into a flat region similar to the blade of a paddle.Altogether, each star is formed, for example, by four tools. Two toolsrespectively enclose an angle of 90°. The blades of the paddles arepositioned diagonally relative to the air stream, which flows throughthe mixer. As a result, a turbulence is created in the air, therebyproviding a good mixing of the solid wood components with the adhesive.Several “stars” formed by the tools are attached to the axis at regularintervals. The solid wood components are then transported through themixer parallel to the axis. In general, the tools are specially designedto cause turbulence in the air near the solid wood components.Propeller-like tools or tools acting as propellers are thereforepreferred.

A curtain is preferably formed from the solid wood components asfollows.

A transport means, such as a conveyor belt and/or a belt weighingmachine, is provided with at least one roller, preferably more than one,roller at the end. The solid wood components are passed through theroller(s). In particular, the rollers are pressed against one another. Agap remaining between two rollers, or between one roller and an adjacentsurface, is, in principle, unproblematic. A kind of curtain or mat isformed from the solid wood components as they pass through the rollers.The form of a curtain is therefore created by the rollers.

In this context, a conveyor belt is used by preference, because thisguarantees a uniform supply of solid wood components, which areespecially provided entirely or predominantly in the form of fibres, tothe rollers. In one embodiment, a belt weighing machine is used tocontrol the rate of supply to the rollers, thereby supplying aparticularly constant quantity of solid wood components to the rollers.According to the prior art, worm screws are routinely used for thetransport of solid wood components in the manufacture of boards.However, the solid wood components leave the worm screws in a relativelyuneven manner. This would form a correspondingly uneven curtain from thesolid wood components. A curtain of uniform thickness and width isadvantageous in order to achieve a uniform distribution of adhesive.This also means that the curtain reliably separates sprayed adhesivefrom downstream tools.

In particular, rollers compressed together or with a gap between themfor the production of the curtain, prevent the solid wood components,especially if these are present entirely or predominantly in the form offibres, from being transported in a wad-like or clump-like manner. Thiswould impair the desired uniform application of adhesive.

In one embodiment, in order process a sufficiently large quantity ofsolid wood components to form a curtain and to achieve a particularlyuniform curtain, more than two rollers, through which the solid woodcomponents are guided to form a curtain, are provided. The rollers arepreferably arranged above one another offset in such a manner that anacute angle is enclosed between the rollers and a transport medium, forexample, a conveyor belt and/or belt weighing machine. Accordingly,sufficient material can be supplied to the transport medium, forexample, the belt weighing machine, in order to process a sufficientlylarge quantity of solid wood components in a uniform manner.

It has already been shown in practice, that a total of four rollers isparticularly advantageous in order to create a curtain from the solidwood components, to which adhesive is subsequently applied by mechanicalmeans.

The opening, through which the curtain consisting of the solid woodcomponents is guided into or in front of the mixer, preferablycorresponds to the maximum width of the mixer housing, for example, thediameter of the named tube, which at the same time forms the walls ofthe mixer. This ensures that the entire width of the mixer is covered bythe curtain. Otherwise, adhesive could be sprayed into the interior ofthe mixer through the remaining openings at the sides of the curtain,and the problems of contamination mentioned above would occur.

If the entire width of the mixer was not covered, adhesive would notonly be sprayed into the mixer, but any solid wood components disposedat the edge would be drawn along more strongly and could form clumps.This would impair the quality of the material and could lead tocorresponding production problems. The material would have to bere-processed in a disadvantageous and cost-intensive manner.

In practice, the lateral walls of the mixer are preferably cooled to 7to 15° C., especially to 10 to 12° C. This means that a layer ofcondensation water is deposited on the walls. Adhesion to the walls isavoided by the layer of condensation water.

The temperatures named above are also suitable for the formation of alayer of condensation water on the interior walls inside the ascendingpipe.

Since a gaseous medium such as air is provided, inter alia, for thetransport of the fibres with the adhesive through the mixer, the nozzlesfor supplying adhesive, in one embodiment of the invention, are disposedat a distance from the housing of the mixer. The nozzles in this caseare disposed in front of an opening of the mixer housing. A gap or anannular gap, through which air is drawn and can therefore be supplied inan appropriate manner, then remains between the nozzles and the opening.Moreover, with this embodiment, air, which is introduced via the gap orannular gap, can be pre-heated in order to achieve a desired temperaturein the mixer, especially to promote a desired activation of the adhesiveat the surface.

In one embodiment, tools in the interior of the mixer are attached to anaxle. The nozzles for supplying the adhesive in this case are arrangedin a ring around the axle, in order to supply adhesive to the fibres ina uniform manner. The fibres or respectively the curtain consisting offibres are/is then preferably transported perpendicular to the axlebetween the nozzles and the tools. In dependence upon the diameter ofthe mixer, the nozzles are arranged in a ring of one or more rows. Witha correspondingly large diameter, the entire opening of the mixer issprayed with adhesive by arranging a second row of nozzles in a ringshape around the axle.

In one embodiment of the invention, glass fibres or synthetic-materialfibres are added in addition to the fibres consisting of solid woodcomponents. These fibres are added especially in the mixer orimmediately in front of the mixer. As a result, particularly good,board-like, moulded parts can be manufactured, for example, as aninterior lining in a motor vehicle. Moulded boards of this kind can beused in the automobile industry, for example, as a hat shelf. In thiscontext, it is sufficient if the layer system is subjected only topreliminary pressing. A final pressing need not be carried out.

The automobile industry does not require moulded parts in a quantitycomparable with the normal, economical production of fibres on a largeindustrial scale. It is therefore more economical to manufacture mouldedparts, especially for use in the automobile industry, together with MDFboards (for the manufacture of panels), in order to utilise thequantities of fibre on a large industrial scale. The wood-fibre boardsprovided for the manufacture of panels have an upper side and a lowerside, which run parallel to one another and are flat. These boards are afew millimetres thick. They do not generally contain synthetic-materialfibres or glass fibres, because no special forms, differing from a flatsurface have to be realised.

In manufacturing moulded parts, sharp edges, for example, as specifiedin the German specialist periodical HK 3/88, page 278, are problematic.Sharp edges are susceptible to damage. Problems of this kind can beavoided or significantly reduced by reinforcement with glass fibres orsynthetic-material fibres.

Moulded parts of the type named are also used in the furniture industry.Moulded parts of this kind are required, for example, for doors, whichare shaped in a special manner for design reasons.

By contrast with boards consisting of fibres, for example, MDF boards orHDF boards, which are used as the carrier board for flooring panels,moulded parts, need only be subjected to preliminary pressing.

Preliminary pressing is carried out at considerably lower pressures thanthe final pressing stage. The preliminary-pressing pressure may be onlyone third of the pressure used in the final pressing stage. The finalpressing stage can be carried out at pressures from 75 to 80 kg/cm².

The proportion of glass fibres and/or synthetic-material fibres in amoulded part is up to 25% by weight, preferably up to 15% by weight, inorder to achieve cost favourable results. At least 1% by weight, byparticular preference, at least 5% by weight of glass fibres should beused.

Even regardless of the other named measures and features according tothe invention, separating the wood fibres, which are used for themanufacture of MDF boards or HDF boards for panels, especially flooringpanels, from the wood fibres for the manufacture of moulded parts, isparticularly economical by comparison with the prior art.

In a further embodiment of the invention, solid wood components providedwith adhesive are arranged in a layer—for example, on a conveyorbelt—and charged with hot steam, for example, by steam shock. Followingthis, the layer is compressed in a press—for example, between twocirculating belts pressed against one another—to form a board. Theinvention is particularly appropriate for the manufacture of fibreboards.

In one embodiment, the two main exterior surfaces of the layer aretreated with steam from the outside. This can be carried out at the sametime as a preliminary pressing or compacting of the layer. For example,the layer of solid wood components are transported between two rigidplates by means of a steam-permeable conveyor belt. One plate isdisposed below the conveyor belt while the other plate is disposed abovethe conveyor belt. The distance between the two plates can be reduced inthe direction of transport, thereby compressing the layer. The layer ischarged with steam via nozzles disposed in the plates. The moisture inthe surface region of the layer is then increased, especially by atleast 2% by weight, for example, up to 4% by weight, and therefore, forexample, from 7% by weight up to 9 to 11% by weight. The temperature ofthe steam is typically 100 to 130° C.

As a result of the steam treatment, the thermal conductivity isincreased towards the middle of the layer. Overall, this improves thepressing performance and therefore reduces the pressing time.

In one embodiment, the layer or the already-compacted layer made fromsolid wood components provided with adhesive can be split to form, so tospeak, two layers one disposed above the other. For this purpose, thelayer is transported, for example, on a conveyor belt. A strip or railis arranged above the conveyor belt and transverse to the conveyor belt,in such a manner that it splits the layer disposed on the conveyor belt.A steam treatment device, which is disposed in this manner between thetwo layers, is connected to the strip or the rail. The adjacent sides ofthe two layers resulting from the splitting, or at least one of these,is steam treated as described above, in order to allow a more rapidpressing time. Following this steam treatment, the upper layer isdisposed on the lower layer. The steam treated layers are transportedinto the press and compressed here to form a board.

The steam treatment means that a direct or indirect rapid heating of thefibres provided with adhesive takes place directly before and/or duringpressing.

When manufacturing panels for flooring, it is important that the panelsprovide hard outer layers and a soft inner layer. As a result, footfallnoise, for example, can advantageously be reduced. If the surface issteam treated in a targeted manner, and the interior region remainsrelatively dry, then the surfaces are compressed in a targeted manner.The cause for this is, inter alia, that moist material can be compressedbetter than dry material. In this manner, the surface regions aretherefore compressed in a targeted manner. The preliminary steamtreatment, also allows a control of the temperature course. Accordingly,harder outer layers by comparison with the middle layer can be achievedin an improved manner.

Furthermore, additives, which contribute to the hardening, can be addedto the steam. In this manner, the desired hard surfaces can be improved,if the surfaces are steam treated before pressing.

If harder covering layers are present, these may be relatively thin.Overall, material can therefore be saved with the same board thickness,because the soft middle layer is manufactured from comparatively lessmaterial.

The invention will now be described in greater detail with reference tothe following diagrams.

FIG. 1 shows a section through a belt weighing machine 1 with a mixer 2located downstream. As indicated by the arrow 3, dried fibres, whichhave been manufactured from wood chips, are supplied to the beltweighing machine 1 via an opening of the housing 4. A bevel 5 guides theincoming fibres towards the belt of the belt weighing machine.

The belt weighing machine registers and controls the quantity ofmaterial, which is transported towards the three rollers 6. The threerollers 6 are arranged above one another and offset in such a mannerthat they enclose an acute angle alpha with the belt weighing machine 1.The fibres disposed on the belt weighing machine are conveyed into thisacute angle. They pass the rotating rollers 6. Accordingly, a curtain isformed from the fibres, which is transported perpendicularly downwardsalong the arrow 7 subject to the force of gravity. In this manner, thecurtain enters the mixer 2 between a plurality of nozzles 8 and tools 9.

The mixer consists of a tubular housing. The housing is formed by adouble wall 10 and 11. An axle 12, to which the tools 9 are attached, isarranged centrally in the interior of the housing. A tool 9 encloses aright angle with the axle 12. In each case, four paddle-like tools 9 arecombined in a star shape. Several of these combined tools are attachedat uniform intervals to the axle 12. The front region, into which thecurtain consisting of fibres is introduced, is free from tools. Thisensures a sufficiently large distance between the tools 9 and thenozzles 8. This distance is required so that the adhesive sprayed fromthe nozzles 8 does not strike the tools directly during operation.

The diameter of the housing of the mixer corresponds to the width of theopening, through which the curtain consisting of fibres is introducedinto the mixer. The width of the curtain is adapted to the width of theopening. The nozzles 8 are arranged in an upper region in a semicirclearound the axle 12. As a result, on the one hand, the curtain isuniformly provided with adhesive and, on the other hand, the adhesiveemerging from the nozzles 8 does not strike parts of the mixer directly.A gap is provided between the nozzles 8 and the housing 10, 11, therebyforming a type of annular gap. Air is drawn in through this annular gap.Means for heating the air drawn in are not shown in the diagram.Accordingly, an air-adhesive mixture is formed. The curtain (in otherwords, a mat formed predominantly or entirely of fibres) provided withadhesive is transported by the air stream through the mixer 2 parallelto the axis 12. The axle and also the tools 9 rotate during transport.At this stage, the adhesive is further mixed with the fibres. A cooledliquid is passed between the two walls 10 and 11 of the double wall tocause the formation of layer of condensation water on the interior wallsin the interior of the mixer.

FIG. 2 shows a front elevation of the mixer parallel to the axle 12. Forreasons of simplicity, only two tools 9 are shown. In particular, FIG. 2shows a single-row, semicircular arrangement of nozzles in the upperregion.

FIG. 3 shows an overview of an embodiment of the method.

Deciduous or coniferous timber in the form of trunk, branches and/orwood from saw mills and industrial timber is used as the startingmaterial. The wood is first cut into wood chips of approximately 20×5 mmin a shredding device 31. These wood chips can also come directly fromthe plantation or from saw mills. The chips can be screened in order toseparate excessively small or excessively large particles. When thechips have been sorted to the correct size, they can be washed to removeadhering foreign matter, (especially, sand and earth). This protects andprevents damage to cutting equipment and other tools in downstreammanufacturing and processing stages.

Sawdust, which is provided in a silo 32, can advantageously be re-used.

The wood components are conveyed by means of conveyor belts from theshredding device 31 and from the silo 32 to a funnel-shapedpreliminary-steam-treatment container.

The supply is typically in the proportion of approximately 6:4 (60% byweight wood chips; 40% by weight sawdust). In this manner, sawdust isalso re-used. This allows a further reduction of costs, because suppliesof raw material are saved. The proportion of wood chips shouldpredominate, because fibres and, at a later stage, fibre mats can beformed from these wood chips, thereby providing mechanical stability. Alower limit for the proportion of sawdust does not therefore need to beobserved.

In the preliminary steam treatment container 33, the wood components aremixed, subjected to preliminary steam treatment and heated to 60 to 70°C. The wood components are then supplied to a boiler 34, for example, bymeans of a packing screw. In the boiler 34, the wood components areboiled for approximately 2 to 3 minutes at a pressure of 11 to 16 barand a temperature from 140 to 180° C. Pressure and temperature areselected in such a manner that a separation into liquid and solid woodcomponents takes place.

The liquid components are separated from the solid components and fedinto a line 35, which is connected to the boiler 34 in a gas-tightmanner.

The solid wood components are supplied to a fibre refining machine 36(refiner or defibrator). The fibre refining machine 36 typicallycomprises a stator and a rotor, which are driven by a motor. Here, thesolid wood components are broken down into fibres.

The fibres, which in one embodiment are mixed with sawdust, are fedpneumatically to a drying tube 37. Reference is made to fibres in thefollowing paragraphs regardless of the above. In the drying tube 37, thefibres are dried at 160 to 220° C. The drying takes place relativelyquickly and in a cost favourable manner, because the liquid woodcomponents have already been removed.

From the drying tube, the fibres are transported into cyclones 38, wherethe steam is separated. The fibres are removed from the bottom. Thetemperature of the fibres is then typically 50° C. Adhesive is thenapplied mechanically at comparatively cool temperatures to the fibres inadhesive-application devices 39. The subsequently glued fibres typicallyhave a temperature of 35 to 40° C.

The glued fibres are then transported into one or more screening devices40. In one embodiment, the screening devices 40 comprise heating devicesto heat the fibres to 55 to 60° C. Increasing the temperature isadvantageous if the boards are to be pressed, for example, attemperatures of 80° C. The pressing stage can therefore be accelerated,because the desired temperature need not be reached exclusively by meansof the heated press. Shorter pressing times lead to increased productioncapacity or smaller procurement costs for the presses with circulatingbelts, because these belts can then be shorter. The space requirementfor presses of this kind is smaller, which also helps to reduce costs.

The pre-glued fibres are then supplied to one or more separating devices41. From the separating devices 41, the pre-glued fibres are transportedto a spreading station 42. The spreading station 42 places the pre-gluedfibres on a conveyor belt. The conveyor belt transports the fibres to apreliminary press 44. Here, the fibres are subjected to preliminarypressing being compressed in this manner. The preliminary presscomprises circulating belts, between which the fibres are passed andtherefore compressed. Following this, the fibres pass through a mouldingtract 45, which comprises various devices, which ensure that the fibresare present in the desired form. In one embodiment, the moulding tractleads towards a steam treatment device 46. Here, the fibres are treatedwith steam from above and/or below. The fibres can be split parallel tothe conveyor belt so that they can be steam-treated in the “interior”.

Finally, the fibres are transported to the main press 47, which consistsof two circulating steel belts pressed one against the other. Pressingtakes place here, for example, at 80° C.

The boards are then sawn by means of a sawing device 48 and transportedto a holding device 49. In the holding device, the boards are held insuch a manner that they do not touch. The boards are cooled in thismanner.

The separated liquid components, which are supplied to the line 35, arecooled within the gas-tight sealed system. When these liquid componentshave been sufficiently cooled, they are either disposed of or suppliedto the adhesive-application device 39.

Following this, the boards are further processed, for example, to formpanels. The boards may then, for example, be coated with papers and thelayer system supplied to a press. In the press, the layer system iscompressed at temperatures above 150° C., for example at temperaturesbetween 180° C. and 230° C. The resins used then harden. The board isfurther sawn and provided with connecting elements by milling. Thepanels can be used as a covering for walls or floors. If they are usedas a floor covering, the panels are provided on the upper, decoratedside with an abrasion-resistant, transparent layer.

1-37. (canceled)
 38. A method of manufacturing a construction elementmade from wood fibers, wood chips and/or sawdust comprising the stepsof: providing said wood fibers, wood chips and/or sawdust, applying anadhesive to said wood fibers, wood chips and/or sawdust, and pressingthe wood fibers, wood chips and/or sawdust provided with said adhesiveto form said construction element.
 39. The method of claim 38, whereinthe step of providing said wood fibers, wood chips and/or sawdustincludes providing at least some of said wood fibers, wood chips and/orsawdust as recycled wood fibers, wood chips and/or sawdust from themanufacture of said construction elements.
 40. The method of claim 39,further including the step of grinding said construction elementsfollowing said step of pressing, and wherein said recycled wood fibers,wood chips and/or sawdust are obtained from said grinding step.
 41. Themethod of claim 38, wherein the step of pressing is done at atemperature below 120° C.
 42. The method of claim 38, wherein the stepof pressing is done at a temperature below 95° C.
 43. The method ofclaim 38, wherein the step of pressing is done at a temperature below60° C.
 44. The method of claim 38, wherein said adhesive includesreactive resins, that may be hardened by cross-linking, selected fromthe group consisting of urea resins, melamine resins, acrylic resins,epoxy resins, polyester resins and mixtures thereof, and the step ofpressing said wood fibers, wood chips and/or sawdust is free ofsubstantial hardening of said adhesive.
 45. The method of claim 44,wherein said construction element comprises from less than about 10% upto about 35% adhesive by weight.
 46. The method of claim 44, whereinsaid wood fibers, wood chips and/or sawdust are broken down into solidand liquid components within a gas-tight system, the liquid componentsbeing separated from the solid components at a temperature in the rangefrom about less than 50° C. up to about 90° C., said liquid componentsbeing added to said adhesive and applied to said solid components toform said construction element.
 47. The method of claim 46, wherein saidadhesive is applied to said wood fibers, wood chips and/or sawdust at atemperature less than 100° C.
 48. The method of claim 47, furtherincluding the step of drying said wood fibers, wood chips and/or sawdustin a drying device at a drying temperature, and wherein the step ofapplying adhesive is performed remote of said drying device at atemperature cooler then said drying temperature.
 49. The method of claim48, wherein the step of applying adhesive includes spraying anadhesive-gas mixture onto said wood fibers, wood chips and/or sawdust.50. The method of claim 49, wherein said adhesive is applied in anamount such that the resulting construction element contains from amount45 kg/m³ to 55 kg/m³ of adhesive.
 51. The method of claim 50, whereinthe step of applying adhesive includes placing said wood fibers, woodchips and/or sawdust onto a belt weighing machine and maintaining aconstant weight ratio of said adhesive applied to said wood fibers, woodchips and/or sawdust.
 52. The method of claim 51, wherein said woodfibers, wood chips and/or sawdust provided with said adhesive are mixedand/or stirred in a cooled wall vessel.
 53. The method of claim 52,wherein the step of applying said adhesive includes initially forming acurtain or a mat of said wood fibers, wood chips and/or sawdust andapplying the adhesive to said curtain or mat.
 54. The method of claim53, further including applying air at a temperature of from about 40° C.to about 70°0 C. together with said adhesive to said wood fibers, woodchips and/or sawdust.
 55. The method of claim 54, wherein the step ofapplying said adhesive includes also applying a hardening agent to saidwood fibers, wood chips and/or sawdust.
 56. The method of claim 55,wherein said adhesive applied to said wood fibers, wood chips and/orsawdust has an outer surface that is hardened by cross-linking.
 57. Themethod of claim 56, further including laminating a finishing componentto said construction element at an elevated temperature and completingthe hardening by cross-linking of said adhesive.
 58. The method of claim44, further including breaking down said wood fibers, wood chips and/orsawdust into solid components and liquid components, adding said liquidcomponents to said adhesive, and applying said adhesive and liquidcomponents to said wood fibers, wood chips and/or sawdust.
 59. Themethod of claim 58, further including cooling said liquid components byat least 30° C. and then applying the liquid components to said woodfibers, wood chips and/or sawdust.
 60. The method of claim 58, whereinsaid liquid components include lignin and hemicellulose, said liquidcomponents comprising up to about 20 percent by weight of said adhesive.61. The method of claim 58, wherein synthetic material fibers and/orglass fibers are added to said wood fibers, wood chips and/or sawdust.62. The method of claim 58, wherein said adhesive applied to said woodfibers, wood chips and/or sawdust has an outer surface that is hardenedby cross-linking.
 63. The method of claim 62, wherein said wood fibers,wood chips and/or sawdust are charged with steam immediately beforepressing.
 64. The method of claim 63, wherein said recycled wood fibers,wood chips and/or sawdust are obtained from the manufacture of MDFand/or HDF boards for flooring panels and molded parts.
 65. The methodof claim 64, wherein said pressed construction element is coated with atleast paper provided with resins and compressed in a press attemperatures above 150° C. to laminate said paper to said constructionelement and complete said hardening by cross-linking said adhesive. 66.A construction element made entirely or predominantly from wood fibers,wood chips and/or sawdust provided with adhesive and compressedtogether, said construction element containing from about 45 to about 55kg/m³ of said adhesive.
 67. The construction element of claim 66,wherein said adhesive comprises non-hardened resins.
 68. Theconstruction element of claim 67, wherein said adhesive is selected fromthe group consisting of urea resins, melamine resins, acrylic resins,epoxy resins, polyester resins or mixtures of the same.
 69. Theconstruction element of claim 68, wherein said construction element is aboard.
 70. The construction element of claim 69, wherein said boardconsists essentially of wood fibers secured together with said adhesive.71. The construction element of claim 68, wherein said constructionelement contains more than 5 percent by weight of said sawdust.
 72. Theconstruction element of claim 68, wherein said construction element hasa density of at least 300 kg/m³.
 73. The construction element of claim68, wherein said construction element has a density of less than 1500kg/m³.
 74. A construction element produced in accordance with the methodof claim
 38. 75. A laminate panel having a plurality of layers includinga carrier board and one or more paper layers, said carrier board beingproduced in accordance with the method of claim
 38. 76. The laminate ofclaim 75, wherein said carrier board has a density greater than 1500kg/m³.